[R-pkg-team] Bug#912254: JS in documentation

[Gordon Ball]

Looking into the ggplot2 documentation issue.

The documentation is generated using `pkgdown`, configured by `_pkgdown.yml` (which can be found in github, but not in the CRAN tarball). It would appear that both the default `pkgdown` templates and the custom tidyverse template used for ggplot2 include references to external javascript in their headers.

In principle, the easiest approach would be to package `pkgdown` and
then patch the default template to reference `/usr/lib/javascript`
instead of remote URLs. It would also be necessary to add some magic to
`dh-r` to detect when pkgdown is used in the build and add the relevant
javascript dependencies.

However, we have a problem that the `_pkgdown.yml` file is not shipped
in the CRAN tarball, so we have insufficient source to rebuild
documentation for this package unless we start using github as the
upstream. I suspect this applies to other packages also.

The following list of packages include a reference to `pkgdown`
somewhere (but I haven't verified whether this means they contain
source-less documentation).